Conventionally roller bearings for linear movement are used, particularly for heavy linearly moving bodies such as in machine tools. Among them, those which use roller bearings for limited linear movement and in which rollers are successively rotatably disposed and engagingly retained in a plate-like retainer have a restriction in the stroke of a linearly moving body, and if such stroke is to be increased, there was a defect that the number of rollers to be engagingly retained in the retainer of the roller bearing for linear movement had to be increased, and thus the size, particularly in the lengthwise direction, became large.
Meanwhile, in the case of a roller bearing capable of making linear movement wherein numerous rollers are not engagingly retained in a retainer, namely, for instance, as shown in FIG. 12, in the case of a prior art endless linear movement roller bearing wherein each adjacent roller 30 has its axis differing 90.degree. alternately, and wherein both ends of the linear paths of load track 31 and return track 32 are in communication, the circularly shaped direction changing paths 33, 33 for smoothly performing the direction changing movement of rollers 30 are arranged in the same plane as the plane of tracks 31, 32, as shown in FIGS. 11 and 12. When comparison is made against the prior art slide bearing and considering at a section perpendicular to the direction of movement of the bearing, since it is impossible to install a preload device, it is impossible to increase the rigidity of the roller bearing comparable to the prior art slide bearing. Also the sectional height or width increases in addition to an increase in weight. Therefore, the characteristics of a linear movement roller bearing of high load capacity, small starting resistance, relatively simple maintenance, capability to be preloaded, etc. could not always be utilized, and there were restrictions in the field of use as well as scope of use. In other words, there was a great demand for a compact endless linear movement roller bearing with high rigidity.
In particular, as shown in FIG. 1, the endless linear movement roller bearing, wherein right angle V groove track surfaces 5, 6 which from load zone are respectively provided on a vertical outer side surface 2 of track rail 1 and on a vertical inner side surface 4 of casing 3 which makes a linear movement and mounts on said track rail 1, and wherein roller 7 endlessly circulates, is superior being capable of supporting the upward and downward load in the equal amount. However, in this bearing, the return hole of square shape has to be positioned at 0.degree. shown by 8a, namely, has to be in the same horizontal plane as track surface 5, 6. Thus, there is a defect that the width of the casing becomes maximum, and moreover, such position overlaps with the preload bolt 10 which horizontally forces bearing plate 9 providing track surface 6. As a result, it was impossible to utilize the previously described superior bearing load characteristics induced by the track surface 5 being provided on the vertical outer side surface 2 and the track surface 6 being provided on the vertical inner side surface 4.